1. Field of the Invention
The present invention relates to a flat cable covering and a flat cable using the same. More particularly, the invention relates to a tape-shaped covering for covering through heat welding so as to embed conductors of a flat cable by holding the same from both sides, which is excellent in heat adhesivity, self-weldability, conductor embedding adaptability, nonflammability, heat resistance, and blocking resistance, and excellent also in environmental adaptability upon disposal or the like, and a flat cable using the same.
2. Description of the Related Art
Flat cables are used in a large quantity at present in various electronic and electric devices and car-mounted devices such as personal computers, liquid crystal display units, game machines, cellular phones, printers and copy machines. Each of these flat cables is generally formed by sequentially laminating a primer coat layer (adhesivity improving layer) or an adhesive layer, and a heat-adhesive resin layer to form a tape-shaped heat-adhesive covering, placing such coverings one on top of the other with the heat-adhesive resin -layer surfaces arranged to face each other, causing them to hold a plurality of conductors in between, and heat and pressurize them for integration.
More specifically, there is known a polyvinyl chloride flat cable manufactured by, for example, laminating polyvinyl chloride resin films serving as heat-adhesive resin layers by the dry lamination method on a side of a substrate film comprising a biaxially oriented polyester film to prepare heat-adhesive coverings, placing these heat-adhesive coverings so as to cause the polyvinyl chloride resin film surfaces serving as heat-adhesive resin layers to face each other, holding a plurality of conductors in between, then, heating and pressurizing the same by means of a heating roll, melting the polyvinyl resin films to embed the plurality of conductors therein, and heat-welding the polyvinyl chloride resin films.
There is also known a polyester resin flat cable manufactured by forming a heat-adhesive resin layer comprising a resin composition containing a saturated polyester resin and a flame retardant, via a primer coat layer on a side of a substrate film such as a biaxially oriented polyester film or the like, placing the manufactured heat-adhesive coverings one on top of the other so as to cause the heat-adhesive resin layer surfaces to face each other, inserting a plurality of conductors, then, heating and pressurizing the same by means of a heating roll, melting the heat-adhesive resin layer to embed the plurality of conductors therein, and causing heat-welding of the heat-adhesive resin layers.
However, although the above-mentioned polyvinyl chloride flat cable is popularly used because of an excellent non-flammability, a film made of a polyvinyl chloride resin forming the heat-adhesive resin layer is low in adhesivity with conductors. Particularly in a high-temperature environment, it poses a problem in that gaps are produced between the film and the conductors, thus causing interlayer peeling. In addition, the afore-mentioned polyvinyl chloride flat cable is poor in bending resistance as a result of the low adhesivity with the conductors. For example, in a bending test or a sliding test, it poses another problem in that the conductors are broken in a very short period of time. Still another problem is that use of the polyvinyl chloride resin film may lead to environmental destruction during disposal after use.
Because the above-mentioned polyester resin flat cable uses a biaxially oriented polyester film as a substrate film, and furthermore, a polyester resin is used as a heat-adhesive resin layer, the cable is poor in non-flammability, and as a result, it is necessary to impart non-flammability by adding a flame retardant in a large quantity to the resin composition forming the heat-adhesive resin layer.
More recently, however, in view of the fact that the use of a filler constituents containing a flame retardant comprising a halogen flame retardant or an organic or inorganic phosphorus compound may cause an environmental problem such as atmospheric pollution or river water pollution during use of the flat cables, or disposal thereof after use, it has become necessary to develop a flame retardant not containing a halogen-based or phosphorus-based flame retardant.
The present invention was developed to solve these problems, and has an object to provide a flat cable covering which is excellent in various properties as a flat cable covering such as heat-adhesivity with a conductor (metal), self-weldability, conductor embedding property, non-flammability, heat resistance, blocking resistance, sliding resistance (bending resistance), does not contain a compound containing a halogen element or a phosphorus-based compound in the constituents, and is excellent in environmental adaptability, and a flat cable using the same.
The aforementioned problems can be solved by the present invention described in the following paragraphs.
More particularly, a first aspect of the invention provides a flat cable covering, having a configuration in which an adhesivity improving layer, a flame-retardant heat-adhesive resin layer comprising a heat-adhesive resin containing a filler which contains a flame retardant, sequentially laminated on at least one side of a heat-resistant substrate film; wherein the heat-adhesive resin mainly comprising a linear saturated polyester resin, and the flame retardant is a mixed-type flame retardant containing at least a hydrated metal compound, antimony oxide and a nitrogen compound.
For the purpose of providing various necessary properties and improve environmental adaptability, the flat cable covering of the invention has a configuration except for a compound containing a halogen element and a compound containing phosphorus. As the heat-adhesive resin, a resin mainly comprising a linear saturated polyester resin, not a polyvinyl chloride resin is used. By excluding flame retardants of chlorine-based, bromine-based and other halogen-based compounds and by using at least a mixed flame retardant comprising a hydrated metal compound, antimony oxide, and a nitrogen compound, it is possible to impart properties such as heat adhesivity necessary for a covering and effective non-flammability.
By adopting the aforementioned configuration, it is possible to provide a flat cable covering in which the heat-resistant substrate film has high heat resistance, insulation, flexibility, bending resistance, and mechanical strength; the adhesivity improving layer ensures solid adhesion between the heat-resistant substrate film and the flame-retardant heat-adhesive resin layer; and the flame-retardant heat-adhesive resin layer imparts various properties necessary as a flat cable covering such as heat adhesivity with conductors, self-weldability, conductor embedding property, non-flammability, blocking resistance, and sliding resistance, with an excellent environmental adaptability.
A second aspect of the invention provides a flat cable covering according to that recited in the first aspect of the invention as described above, in which the content of the filler containing the flame retardant in the flame-retardant heat-adhesive resin in which a range of from 60 to 80 wt. %; the filler containing the flame retardant has a content of the hydrated metal component within a range of from 30 to 45 wt. %, a content of antimony oxide within a range of from 10 to 30 wt. %, and a content of a nitrogen compound within a range of from 2 to 10 wt. %.
From among the above-mentioned fillers containing flame retardants, at least one of hydrated metal compounds, antimony oxide and nitrogen compounds is used. Apart from this, a flame retardant other than the above, or an organic or inorganic filler such as a blocking inhibitor may be appropriately selected and used, so far as it does not contain a halogen element or phosphorus.
The content of the filler containing the flame retardant in the flame-retardant heat-adhesive resin layer should preferably be within a range of from 60 to 80 wt. % relative to the resin layer as a whole. A filler content of under 60 wt. % or over 80 wt. % is not desirable, because a content of under 60 wt. % leads to shortage of nonflammability, and a content of over 80 wt. % results in a decrease in heat adhesivity.
Among fillers containing the flame retardants, the contents of the hydrated metal compound, antimony oxide and the nitrogen compound relative to the resin layer as a whole should preferably be such that, within a range of from 30 to 45 wt. % for the hydrated metal compound; from 10 to 30 wt. % for antimony oxide; and from 2 to 10 wt. % for the nitrogen compound. The hydrated metal compound has a remarkable flame retarding effect, but an excessively high content impairs heat adhesivity. It should therefore be preferably up to 45 wt. %. Antimony oxide, which cannot give a remarkable flame retarding effect by itself, but is excellent in effect as a flame retarding assistant. It should therefore preferably be contained within a range of up to 30 wt. %. The nitrogen compound, which has an important effect but is high in cost. It is therefore effective to use the nitrogen compound within a range of up to 10 wt. %, preferably simultaneously with the above-mentioned hydrated metal compound. A combination of at least flame retardants such as a hydrated metal compound, antimony oxide, and a nitrogen compound provides an excellent flame retarding effect.
When the contents of the hydrated metal compound, antimony oxide and the nitrogen compound are under the specified ranges, respectively, there is unavailable a sufficient nonflammability.
From the point of view of flame retarding effect and working adaptability, the particle size of these flame retardants should preferably be within a range of from 0.01 to 15 xcexcm in all cases.
By adopting the aforementioned configuration, therefore, it is possible to impart certainly a satisfactory nonflammability to the flat cable covering in addition to the advantages of the invention as described in the first aspect of the invention, without decreasing the properties other than nonflammability.
A third aspect of the invention provides a flat cable covering according to that recited in the first and second aspects of the invention as described above, in which the hydrated metal compound of the flame retardant is aluminum hydroxide; antimony oxide is antimony trioxide; and the nitrogen compound is melamine sulfate.
Among the above-mentioned hydrated metal compound, antimony oxide, and the nitrogen compound serving as flame retardants, aluminum hydroxide as a hydrated metal compound, antimony trioxide as an antimony oxide, and melamine sulfate as a nitrogen compound are particularly preferable because of the possibility to provide more remarkable flame retarding advantage with slight contents, respectively.
By adopting this configuration, therefore, it is possible to achieve a more excellent nonflammability of the flat cable covering in addition to the advantages of the invention as described as to the first and second aspects of the invention.
A fourth aspect of the invention provides a flat cable wherein flat cable coverings according to any one of the first to third aspects of the invention are placed one on top of the other on both sides of each of a plurality of conductors arranged in parallel with each other so that surfaces of the flame-retardant heat-adhesive layer face each other, and the flat cable is formed by heat-bonding so as to embed the conductors through heating and pressurizing from outside.
By adopting this configuration, it is possible to provide at a high productivity a flat cable which is excellent in properties necessary as a flat cable such as sliding resistance (bending resistance), heat resistance, nonflammability, and insulation, and in environmental adaptability, since excellent properties as a flat cable covering and environmental adaptability are imparted to the flat cable.